We propose to develop a novel method for the diagnosis of Helicobacter Pylori. The diagnosis of H. Pylori is a high medical priority because: this bacterium infects approximately 50% of the world's population; causes peptic ulcer disease, gastric cancer, a form of lymphoma (MALToma) and likely several other diseases; and is treatable with antibiotics, but if this organism is not eradicated, patients remain at risk for serious complications. Of the many diagnostic tests for H Pylori, the urea breath test (UBT) is the best: it is simple, noninvasive, has excellent sensitivity and specificity and can diagnose current infection. It is based on the ability of H pylori to convert urea to CO2 and ammonia using its enzyme urease. Current embodiments of UBT employ 13C-urea and detect labeled CO2 in breath. Current UBTs are not extensively used because they are costly and not available at the point-of-care. We propose to develop a simple UBT using as substrate unlabeled urea and detecting ammonia in breath with a nanosensor incorporated in a very simple device. Our preliminary work fully supports the feasibility of our approach. Our specific aims are to 1) Perform UBTs in patients using our sensor to determine NH3, and 2) Develop a portable breath analyzer for the detection of H. pylori based on the determination of NH3 in human breath. The proposed UBT will be simple, inexpensive, noninvasive and available at the point-of care. Thus it will make widely available a simple device for the diagnosis of H pylori and the monitoring of treatment efficacy.